1. Field of the Invention
The present invention generally relates to focal plane arrays of photodetectors, particularly infrared and far-infrared detectors, and more specifically to methods and means for comprehensive testing and comparing of all types of arrays for use in infrared imaging systems.
2. Description of Prior Art
In the visible light spectrum target detection and imaging systems have developed rapidly, due to their use of silicon based technology. This technology has been highly developed for all types of integrated electronic circuits. In particular charge coupled devices (CCD's) are readily married to silicon detector arrays to form highly sophisticated single chip detectors of excellent quality, that are easily mass produced.
Infrared or IR systems, which are invaluable to military and related civilian applications, have developed much more slowly. The best detectors have been photodiodes. Silicon photodiodes, however, work well only at wavelengths vary close to the visible. At lower wavelengths these diodes require compounds of elements from columns II-VI of the periodic table. At far-infrared frequencies, i.e. about 8 to 14 micron wavelengths, the best detector material appears to be mercury cadmium telluride. Such detectors vary in complexity from a single diode with elaborate scanning mirrors to a staring array using thousands, and eventually millions, of diodes. Unfortunately, these diodes require cooling to liquid nitrogen temperature to eliminate thermal noise.
Another main class of detector or imaging systems is denoted as uncooled and this class includes detectors based on ferroelectric, pyroelectric or other temperature induced changes in materials that can be manifested electronically. Such detectors may require a positive rather than a negative temperature bias, although materials that operate at room temperature are available. It thus can be seen that testing land comparing these diverse systems is rapidly becoming a major problem. In U.S. Pat. No. 4,875,004 for a "HIGH SPEED CHARACTERIZATION TECHNIQUE" by Phillip R. Boyd issued on Oct. 17, 1989; there is shown a test set which characterizes the HgCdTe array chip portion of a detector, using an E-beam generator, before the chip is mated to a silicon CCD readout to form a complete detector. An automated test set is needed that can characterize each complete detector or pixel generator, under ranges of normal operating conditions, and which interfaces a computer to store and process the data in useful statistical formats.